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Uses and Abuses of the Energy-Time Curve

Two basic aspects of the familiar Heyser energy-time curve (ETC) as applied to electroacoustic system measurements are addressed, 1) its inherantly acausal nature, which means that it should not be interpreted literally as representing the energy flow of a physical system, and, more importantly, 2) the way in which the appearance of an actual ETC is affected by the detailed nature of the data from which it is computed, and especially by any frequency-domain window that is used in its computation. Theoretical and experimental data are used to illustrate the variety of behavior that can occur, and show how the processing can either enhance or falsify the measurement.